Insertional Achilles tendinopathy (IAT) is a painful and common disorder that is difficult to treat. Standard physical therapy interventions that work well for other forms of Achilles tendinopathy are only ~50% effective for IAT, and patients who fail physical therapy require surgeries that are expensive, entail long recovery times and often lead to complications. Thus, there is a need to develop novel and effective treatments to improve clinical outcomes for IAT patients. A critical step in this process is to establish a tool or accurately monitoring the efficacy of conservative and non-conservative care. IAT is thought to be caused by compressive stress due to impingement of the tendon on the heel bone as the ankle rotates, and our preliminary studies support this theory. Thus, we hypothesize that tracking compression of the Achilles tendon against the heel as the ankle rotates is a useful tool for assessing the severity of IAT. In preliminary work, we have shown that we can quantify compression of the Achilles tendon onto the heel by analyzing ultrasound images taken while the ankle rotates. In Aim 1, we propose to apply this technique to test whether the extent of compression in IAT tendons is larger than in healthy tendons. In Aim 2, we will investigate whether the extent of compression in IAT tendons is associated with tissue-scale structural and mechanical alterations. Finally, in Aim 3 we will test whether self-reported function in IAT patients is better correlated with our ultrasound-based measurements of tendon compression than with standard clinical measures of heel geometry and muscle stiffness, two factors that may contribute to impingement of the Achilles tendon on the heel. The findings of this study will define a critical threshold for damaging compression in the Achilles tendon that will guide novel, targeted strategies designed to reverse IAT. Furthermore, the inexpensive and non- invasive tool established in this proposal will enable longitudinal monitoring of treatments for this IAT tht may help improve outcomes for IAT patients. Project Description Page 1